Porous inorganic solids have found great utility as catalysts and separations media for industrial applications. The openness of their microstructure allows molecules access to the relatively large surface areas of these materials that enhance their catalytic and sorptive activities. The porous materials in use today can be sorted into three broad categories using the details of their microstructure as a basis for classification. These categories are the amorphous and paracrystalline materials, the crystalline molecular sieves and modified layered materials. The detailed differences in the microstructures of these materials manifest themselves as important differences in the catalytic and sorptive behavior of the materials, as well as in differences in various observable properties used to characterize them, such as their surface areas, the sizes of pores and the variability in those sizes, the presence or absence of X-ray diffraction patterns and the details in such patterns, and the appearance of the materials when their microstructure is studied by transmission electron microscopy and electron diffraction methods.
The M41S family of mesoporous molecular sieves is described in J. Amer. Chem. Soc., J. S. Beck et al., 1992, Vol. 114, Issue 27, pp. 10834-10843. Members of the M41S family of molecular sieves include MCM-41, MCM-48 and MCM-50. A member of this class is MCM-41 whose preparation is described in U.S. Pat. No. 5,098,684. MCM-41 is characterized by having a hexagonal structure with a unidimensional arrangement of pores having a cell diameter greater than about 13 Angstroms. MCM-48 has a cubic symmetry and is described for example in U.S. Pat. No. 5,198,203. MCM-50 has a layered or lamellar structure and is described in U.S. Pat. No. 5,246,689.
The M41S family mesoporous molecular sieves are often prepared from aqueous reaction mixtures (synthesis mixtures) comprising sources of appropriate oxides. Organic agents, such as surfactant(s), are also generally included in the synthesis mixture for the purpose of influencing the production of the M41S family mesoporous molecular sieves having the desired structure and channel size. After the components of the synthesis mixture are properly mixed with one another, the synthesis mixture is subjected to appropriate crystallization conditions in an autoclave. Such conditions usually involve heating of the synthesis mixture to an elevated temperature possibly with stirring. After crystallization is complete, the crystalline product is recovered from the remainder of the synthesis mixture, typically by filtering the crystals and then washing the crystals with water to remove the mother liquor and other residual synthesis mixture components. The crystals are then normally dried and subjected to high temperature calcination, e.g., at 540° C., particularly to remove any organic agent which may otherwise block the pores of the molecular sieve.
The process of synthesizing the M41S family mesoporous molecular sieve utilizes expensive organic surfactants. Moreover, significants costs are incurred for disposal of surfactant-containing wastewater generated in the crystallization, filtration, and washing. Thus a need exists for a more efficient and cost-effective process of manufacturing M41S family molecular sieves which reduces both the amount of water used and wastewater produced. This disclosure provides a process of manufacturing M41S family molecular sieves from forming mixtures of high solids content, using a reactor having a high intensity mixer. The process does not require filtering the reaction mixture after crystallization or washing the molecular sieve product before calcinations. Accordingly, the process combines the advantages of reduced cost, shorter crystallization time and higher yield with the minimization of wastewater generated during the molecular sieve manufacture.
U.S. Patent Application No. 60/899,785, filed Feb. 6, 2007 (priority claimed in WO2008/097481, dated Aug. 14, 2008), relates to a method for synthesizing a mesoporous molecular sieve composition, in which at least a portion of the solvent or solvent mixture in the reaction mixture comprises wastewater from processing of the mesoporous molecular sieve made in previous synthesis batches, e.g., the mother liquor(s), the washing liquid(s), the cleaning liquid(s), and any combination thereof.
U.S. Patent Application Publication No. 2010/0280290 relates to a method of making M41S materials using synthesis mixture having high solids content and reducing wastewater containing surfactant(s), such as, mother liquor, formed in the synthesis, as well as minimizing or eliminating filtrating and/or washing step(s) of the synthesis.
WO 2009/055215 teaches making M41S materials from high solids forming mixtures (20% to 50 wt %) which can be recovered without a purification step (filtration and/or washing). Crystallization can be carried out under static or agitated conditions (paragraph 0083) but no disclosure or suggestion of using high intensity mixers for M41S crystallization is made.
U.S. Pat. No. 6,664,352 to Fredriksen teaches preparing metallocene catalysts by mixing catalyst and porous particulate support in a mechanically fluidized state with a catalyst material. The process uses a mixer having horizontal axis counter-rotating interlocking mixing paddles where paddles on different but preferably parallel rotational axes pass through a common mixing zone. The mixer can have a Froude number of from 1.05 to 2.2. No suggestion or disclosure is made for using this mixer in the crystallization of molecular sieves.
U.S. Pat. No. 6,521,585 to Yamashita et al. discloses the production of crystalline alkali metal silicate granules which are stably formulated in detergents. Temperature-controllable agitating mixers carry out mixing crystalline alkali metal silicate with detergent at a Froude number of 1 to 12 to control particle size distribution of granules. Mixers include horizontal, cylindrical blending vessels having agitating impellers on an agitating shaft.
Various mixers useful to mix slurries, pastes, and plastic bodies are described in “Principles of Ceramics Processing,” Second Edition, James S. Reed, John Wiley & Sons, Inc., 1995, at pages 347-354.